The grading of objects such as fish and marine species such as capilion and herring can be a problem. The reason being their small size and the volume to be processed at each time combined with that the quality of fish deteriorates quickly if not stored at sub zero temperature. The grading therefore has to be highly efficiently The purpose of the grading is primarily to separate the species by size and/or the sex. Such grading can often result in substantial increases in value as female capilion filled with eggs is much more valuable than the male species. No feasible methods are currently known for such grading.
There are machines, which are capable of grading fish and other objects by size, especially thickness. These include belt and roller machines of various types and shaker graders. The best known, are belt machines, which pull the object between two slanting belts which form a transport channel. These machines frequently have many channels. There are also roller machines where two or more parallel rollers form lanes slanting in the direction of movement of the object. The rollers rotates and the object moves forward. The distance between the rollers is greater at the output end than the input end so that the smallest units of objects are first to fall between the rollers while the larger units fall later. In this way, grading by thickness corresponds to increased distance between the transport belts or rollers. This applies generally to machines based on designs where the distance between lanes is greater at the out-feed end than the in-feed end.
Numerous patents are known which in one way or another attempt to solve this complex problem. U.S. Pat. No. 1,373,812 from 1921, is known which describes a spinning feeding mechanism for grading of sardines. U.S. Pat. No. 2,314,479 from 1943, is known which concerns grading of fish by size and its handling during processing. Norwegian patent, No. 132.917 from 1974, is known which concerns transport and grading, especially of shrimp. British patent, No. 2.140.712A from 1983, is known which concerns grading of plums. PCT patent application No. WO 88/06495 from 1988 is known, which concerns grading of shrimp and related materials. U.S. Pat. No. 4,723,660 from 1988 concerns apparatus for transport and grading of material. U.S. Pat. No. 2,547,473 from 1951 is known concerning grading of fruit by size. Another U.S. Pat. No. 1,251,093 from 1917 concerns grading of fruit and vegetables. Another U.S. Pat. No. 1,204,685 is known concerning grading of fruit and a packaging bench. Another U.S. Pat. No. 1,178,006 concerns grading of fruit and vegetables. Finally, PCT application from the present applicant from 1996 concerns a method and apparatus for grading of fish and other materials by size.